Some of mine: Joining a fraternity in college; joining the particular fraternity in college. Deciding to finally get sober. Marrying the woman I married. Deciding to get a divorce.
A lot of other things were not so much critical decisions (although they had a great impact on my life) as much as they were evolutionary. Not doing homework in high school was not some big decision, but when I was applying to schools, it took Harvard and Yale out of the picture. I went to school where I was accepted.
I have to remind myself that if I had taken some other paths, it would still be me on that path. So if had gone to Harvard like I really wanted to, I would have had alcohol affect my academics the same way, just at a more prestigious level.
What do you call an alcoholic dropout from Harvard? Unemployed.